The present invention relates generally to a composite forming process such as a pultrusion process and more particularly, to an improved manner of positioning a plurality of reinforcement strands including at least one spliced strand in a desired spatial relationship prior to entering a forming a die.
In a conventional pultrusion process, strands are pulled from a plurality of reinforcement input packages, such as glass packages, wetted in a resin bath and fed to one or more shaping dies to form a composite part. For example, 20 packages may be provided on a creel, thus providing 20 strands for the pultrusion process. The creel is positioned ahead of the resin bath. When one package becomes depleted, the operator splices the strand end from the depleted package to the strand end of a new package via a conventional splicing technique, such as an air splice, a glue splice or an overwrap splice. See for example, U.S. Pat. Nos. 4,428,992 and 4,803,762, the disclosures of which are incorporated herein by reference. Typically, the splicing is done while the pultrusion process is ongoing.
In the past, the reinforcement strands, including any spliced strands, ran over a transversely extending cylindrical rod prior to coming together in a bundle and entering a pultrusion die. Thus, the position of any splice in the bundle entering the die varied, depending on the position of the spliced strand relative to the others in the die. In the case where the spliced strand was an xe2x80x9couterxe2x80x9d strand, any loose fibers or filaments at the splice oftentimes would catch on an edge of the die, causing those fibers to be stripped back by the die. After fibers catch on the die edge, the process must be stopped.
Alternatively, once a package had been depleted, instead of splicing together fibers from two packages, the pultrusion process is stopped and all packages, including those still having strand material, are replaced. The amount of material initially provided on each of a plurality of packages typically varies. If all packages are replaced when a first package is depleted, strand material remaining on the other packages is scrapped. Hence, this replacement process is undesirable for at least two reasons. First, the process is inefficient as the pultrusion line is stopped during package replacement. Second, the process is costly, due to reinforcement material on the non-depleted packages being scrapped.
Accordingly, there is a need for an improved process and apparatus for splicing together strand ends and positioning the spliced strand at an appropriate location within a bundle of strands prior to the bundle entering a pultrusion-forming die such that fibers or filaments at the splice do not catch on an edge of the die.
This need is met by the present invention, wherein an improved process and apparatus are provided for centrally positioning a spliced reinforcement strand within a bundle of reinforcement strands entering a forming die. As the splice enters the die, it is surrounded by uninterrupted strand material. Consequently, any loose filaments or fibers at the splice do not contact and become snagged on an edge of the forming die as the splice enters the die. Furthermore, since the splice is located on a central axis of the resulting workpiece, the overall bending strength of that workpiece is enhanced.
In accordance with a first aspect of the present invention, a process is provided for positioning a plurality of reinforcement strands including at least one spliced reinforcement strand in a desired spatial relationship prior to entering a forming die. The process comprises the steps of: positioning a plurality of uninterrupted reinforcement strands moving toward a forming die so that the uninterrupted strands extend from a first location upstream of the forming die to the forming die in a space-apart converging configuration; and positioning at least one spliced reinforcement strand so that it extends generally centrally through the center of the converging configuration of the uninterrupted strands.
The uninterrupted and spliced strands are formed from fibers selected from the group consisting of E-glass fibers, S-glass fibers, graphite fibers, aramid fibers, carbon fibers, metallic fibers and ceramic fibers.
The step of positioning a plurality of uninterrupted reinforcement strands may comprise the steps of providing a jig having a plurality of circumferentially disposed apertures and passing the uninterrupted strands through the apertures. The jig also has at least one aperture for receiving the at least one spliced reinforcement strand. The jig may comprise a plate having eyelets therein which define the plurality of apertures. Alternatively, the jig may comprise a plate having a plurality of open U-shaped members that define the plurality of apertures.
The step of positioning at least one spliced reinforcement strand may comprise the steps of: providing a guide element located along or adjacent to a centerline of the forming die; passing the at least one spliced reinforcement strand through an aperture in the jig; and passing the at least one spliced strand through the guide element after the strand has passed through the jig aperture. The guide element may comprise a rod having an open helical end.
In accordance with a second aspect of the present invention, a pultrusion process is provided. It comprises the steps of: coating a plurality of uninterrupted reinforcement strands and at least one spliced reinforcement strand with a polymeric material; positioning the uninterrupted reinforcement strands so that they extend from a first location upstream of a forming die to the forming die in a space-apart converging configuration; positioning the at least one spliced reinforcement strand so that it extends generally centrally through the center of the converging configuration of the uninterrupted strands; and passing the uninterrupted and spliced strands through the forming die.
The uninterrupted and spliced strands are formed from fibers selected from the group consisting of E-glass fibers, S-glass fibers, graphite fibers, aramid fibers, carbon fibers, metallic fibers and ceramic fibers.
The step of positioning a plurality of uninterrupted reinforcement strands may comprise the steps of providing a jig having a plurality of circumferentially disposed apertures and passing the uninterrupted strands through the apertures. The jig also has at least one aperture for receiving the at least one spliced reinforcement strand. The jig may comprise a plate having eyelets therein which define the plurality of apertures. Alternatively, the jig may comprise a plate having a plurality of open U-shaped members that define the plurality of apertures.
The step of positioning at least one spliced reinforcement strand may comprise the steps of: providing a guide element located adjacent to or along a centerline of the forming die; passing the at least one spliced reinforcement strand through an aperture in the jig; and passing the at least one spliced strand through the guide element after it has passed through the jig aperture. The guide element may comprise a rod having an open helical end.
In accordance with a third aspect of the present invention, an apparatus is provided for positioning a plurality of uninterrupted reinforcement strands and at least one spliced reinforcement strand in a desired spatial relationship prior to entering a forming die. The apparatus comprises first and second guide structures. The first guide structure is positioned at a first location upstream of the forming die for receiving the uninterrupted strands and the at least one spliced reinforcement strand. The uninterrupted strands extend from the first guide structure to the forming die in a space-apart converging configuration. The second guide structure is positioned at a second location between the first location and the forming die for receiving the at least one spliced reinforcement strand from the first guide structure. The second guide structure positions the at least one spliced strand so that it extends generally centrally through the center of the converging configuration of the uninterrupted strands.
The first guide structure may comprise a jig having a plurality of circumferentially disposed apertures for receiving the uninterrupted strands and the at least one spliced strand.
The second guide structure may comprise a guide element positioned adjacent to or along a centerline of the forming die.